1. Field of the Invention
This invention relates to a brake master cylinder, and more particularly to a brake master cylinder having a body made of resin material.
2. Description of the Prior Art
Conventionally, a brake master cylinder having a body of resin material has been proposed to lighten the weight of a vehicle. Since the body is made of resin material, there is the possibility that the inside wall of the resin body may be damaged by the sliding movement of a piston positioned within the body. This results in a reduction in the sealing effect and in leakage of fluid.
In order to reduce the above drawbacks, a metal tube has been further proposed to be positioned within the inside wall of the resin body as disclosed in the British Patent Specification No. 1,051,512. The resin body is formed by a molding member in the form of a sleeve-like portion positioned around the metal tube and having a plurality of grooves to thereby securely position the metal tube within the resin body. However, in this prior brake master cylinder, the cost in manufacturing the metal tube is relatively high since the metal tube extends for the whole length of the inside wall of the body and the plurality of grooves have to be formed therein. Furthermore, a gap may occur between the resin body and the metal tube due to the difference in the rate of thermal expansion therebetween especially when the brake master cylinder is at a high temperature. This results in leakage of fluid. If the inside wall of the metal tube is damaged by twisting of the piston or the like, there also is a disadvantage that both the body and metal tube have to be exchanged because the metal tube is integrally formed with the body.